Regenerated cellulose fiber

ABSTRACT

The invention relates to a regenerated cellulose fiber ( 1″ ) the cross-section of which comprises an oblong, essentially flat section ( 3 ). The fiber according to the invention is characterized in that at least one limb ( 4, 5, 6, 7 ) branches off from the oblong section, wherein the length of said limb is at most 40% of the length of the oblong section ( 3 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a regenerated cellulose fiber which is obtained by the viscose process.

2. Description of Related Art

For sanitary applications such as, for example, tampons or absorbent bodies in general, fibers with a particularly high liquid storage capacity are desirable in order to thus allow an absorption capacity as high as possible of the sanitary product.

Fiber materials according to the prior art which usually are used for the production of tampons are regular viscose fibers, so-called trilobal viscose fibers and cotton. The specific absorption capacity of said fibers according to the so-called Syngina test as described further below is about 4.0 g/g for cotton, 4.5 g/g for regular viscose and 5.2 g/g for trilobal viscose fibers.

The aim of tampon producers is to achieve a particular degree of absorption with a minimum expenditure of fiber material and money.

While cotton is slowly becoming obsolete as a fiber material for tampons because of its insufficient absorption capacity, trilobal fibers are much more expensive to produce and it is far more difficult to process them into tampons, as compared to regular viscose.

Many different approaches for increasing the absorption capacity of cellulose fibers have been reported:

-   -   a chemical modification by grafting monomers onto the cellulose         fiber     -   a chemical modification by incorporating absorbent polymers such         as carboxymethyl cellulose, chitosan, cellulose carbamate,         alginate or guaran into the cellulose fiber matrix     -   a physical modification of the fibers such as, e.g., hollow         fibers or collapsed hollow fibers, as known, for example, from         U.S. Pat. No. 4,129,679, or     -   multi-limbed fibers (so-called “trilobal” fibers) which are         obtained by using spinnerets having multi-limbed extrusion holes         with at least 3 limbs having a length-to-width ratio of 2:1 to         10:1, as known, for example, from EP-A1 0 301 874.

The disadvantage of a chemical modification of the cellulose fiber is that a costly and time-consuming toxicological and physiological test procedure is necessary for very delicate medical applications such as those of tampons and the occurrence of the toxic shock syndrome (TSS) keeps most tampon producers from using chemically modified fiber materials although the chemicals are possibly regarded as safe.

The disadvantage of hollow fibers and collapsed hollow fibers is that they are difficult to produce because of their high water retention capacity, as a result of which the fibers swell strongly during washing and adhere to each other during drying because of the formation of hydrogen bonds, which makes them brittle in the dry state, soapy in the wet state and renders it difficult to break them up and process them into a carded fabric.

In recent years, the use of multi-limbed, in particular trilobal fibers has experienced a steady increase.

The production of multi-limbed viscose fibers has been described, for example, in the U.S. Pat. Nos. 5,634,914 and 5,458,835 and in EP-A1 0 301 874. The process disclosed therein describes the spinning of a commonly used viscose, which may contain a certain amount of a modifier known from prior art, through extrusion holes of a multi-limbed shape, in particular a trilobal shape, into a conventional spinning bath. The essential feature of said process is that the shape of the multi-limbed extrusion holes in the spinneret is similar to the desired shape of the cross-section of the filaments. According to the teachings of those documents, the geometry of the spinneret hole determines the shape of the fiber cross-section, and a particular length-to-width ratio of the fiber cross-section can be obtained by designing the extrusion holes appropriately.

Moreover, the prior art with regard to multi-limbed fibers teaches that such multi-limbed fibers have an absorption capacity which is enhanced in comparison to that of viscose fibers according to the prior art, namely in particular in tampons, and that such fibers must have at least 3 limbs and that each limb of those fibers must exhibit a length-to-width ratio of at least 2:1, most preferably of from 3:1 to 5:1. The larger the length-to-width ratio, the higher would be the proportion of free volume and the absorption capacity of the fibers, provided that the limbs are not so long and thin that they will bend back onto themselves.

In those documents, it is also mentioned that, under the conditions of slow regeneration spinning, even higher absorption capacities of the multi-limbed fibers can be achieved, for example, by lowering the acid level and/or increasing the sulphate level and/or adding a viscose modifier.

The fact that hollow spaces in the cross-section of viscose fibers increase the absorption capacity of said fibers and of the products produced therefrom is furthermore known from U.S. Pat. No. 4,362,159.

From WO 2004/085720 A, a solid regenerated standard viscose fiber is known which has a cross-section the area of which is larger than the area of the largest equilateral triangle inscribed into said cross-section by a factor of less than 2.50 times, preferably less than 2.40 times, particularly preferably less than 2.25 times, and which exhibits a Syngina absorption capacity of more than 6.0 g/g fiber, as defined below.

WO 2004/005595 A describes an absorbent standard viscose fiber having an irregularly lobed cross-section. Further viscose fibers with irregular cross-sections are described in U.S. Pat. No. 4,129,679 and GB-A 1,333,047.

U.S. Pat. No. 6,403,217 B1 describes a variety of die configurations for the production of fibers having modified fiber cross-sections according to the melt spinning process. Melt spinning processes differ fundamentally from the wet spinning process used in the viscose process.

Conventional trilobal fibers as known from EP 0 301 874 A exhibit a high absorption capacity. One the one hand, this is attributable to the high stiffness caused by their geometrical structure, which stiffness increases the stability of the pores formed by trilobal fibers and thus enables the storage of large amounts of liquid. On the other hand, the Y-structure also affects the packing density of the fibers: Because of their sterically demanding structure, hollow spaces are automatically formed which are larger than when, for example, a round fiber of the same structure is used.

Due to the coarse pore structure, the capillarity in Y-fibers as known from prior art is relatively minor. For absorbent bodies with a faster absorption performance and a better distribution effect, the formation of a larger number of hollow spaces, which, in exchange, are smaller, would be advantageous.

In order to overcome the above-mentioned disadvantages of known absorbent viscose fibers, according to the invention, a regenerated cellulose fiber is provided the cross-section of which comprises an oblong, essentially flat section and which is characterized in that at least one limb branches off from the oblong section, wherein the length of said limb is at most 40% of the length of the oblong section.

The object of the invention is also achieved by a fiber bundle which contains a plurality of cellulose fibers according to the invention.

Further aspects of the present invention relate to a process for the production of the cellulose fiber according to the invention as well as to the use of the cellulose fiber according to the invention and of the fiber bundle according to the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the attachment of two trilobal cellulose fibers known, for example, from EP 0 301 874.

FIG. 2 shows the attachment of several fibers having a flat cross-section.

FIG. 3 shows the cross-section of a fiber according to the invention.

FIG. 4 shows the attachment of several fibers according to the invention.

FIG. 5 shows the retention of water by a fiber according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

It has been found that, in case of a cellulose fiber the cross-section of which comprises an essentially flat, oblong section comprising at least one limb protruding therefrom, the pore size of products produced from a plurality of such fibers can be influenced favorably as compared to trilobal fibers.

The limb is preferably arranged essentially at a right angle with respect to the oblong section.

Particularly preferred are embodiments in which several branch-off limbs are provided.

Advantageously, the limbs can thereby branch off from the oblong section in both directions.

It is likewise preferred that the total_([AAR1)] length of the branch-off limbs does not exceed the length of the oblong section.

At least a portion of the limbs, preferably all the limbs, may have a ratio of length to width of from 2:1 to 10:1.

At least a portion of the limbs, preferably all the limbs, may have a width which is smaller than the width of the flat section.

The entire curvature of the flat section preferably has at most 120°. Even when the spinning is effected through dies with a flat spinning opening, a certain curvature may occur in the resulting flat fibers (or, respectively, in the flat section which is provided according to the invention). The angle defined by the endpoints of the flat section as well as the point of the flat section which is located farthest from the imaginary straight line through said endpoints is thereby regarded as the curvature.

The fiber titer of the fiber according to the invention may range from 1.3 dtex to 10 dtex.

The cellulose fiber according to the invention can be provided in the form of a staple fiber, a short-cut fiber or as a filament tow.

The invention also relates to a fiber bundle containing a plurality of regenerated multi-limbed cellulose fibers, wherein at least 10%, preferably at least 20%, particularly preferably at least 50%, of the multi-limbed cellulose fibers are provided in the form of a cellulose fiber according to the invention. In the fiber bundle according to the invention, also essentially all of the multi-limbed cellulose fibers contained therein may be provided in the form of a cellulose fiber according to the invention.

A plurality of fibers can be understood as a “fiber bundle”, for example, spun rayon (a plurality of staple fibers), a strand of continuous filaments or a bale of fibers.

Preferably, essentially all of the multi-limbed cellulose fibers contained in the fiber bundle are provided in the form of the cellulose fiber according to the invention and, respectively, the cross-sections of the multi-limbed cellulose fibers contained in the fiber bundle are essentially equal.

The fiber bundle may contain further fibers, for example, cellulose fibers which are not multi-limbed, but also fibers of a different origin, e.g., from other polymers.

The process according to the invention for the production of a regenerated cellulose fiber and, respectively, of a fiber bundle according to any of the preceding claims comprises the steps of

-   -   providing a viscose spinning mass     -   spinning the viscose spinning mass through at least one opening         of a spinneret into a spinning bath, whereby filaments are         formed,

and is characterized in that the opening of the spinneret comprises a slot-shaped section from which at least one limb branches off the length of which is at most 40% of the length of the slot-shaped section.

Optionally, the process according to the invention may comprise the step of mixing the fibers produced by the process with other fibers, for example, conventional multi-limbed fibers, fibers which are not multi-limbed and/or fibers of a different origin, e.g., from other polymers.

Preferably, the smaller angle between the limb and the slot-shaped section has between 30° and 90°, particularly preferably between 60° and 90°.

Preferably, the process according to the invention is configured such that the spinneret comprises several openings, with all the openings having essentially the same shape. In this way, the preferred configuration, namely that all fibers have essentially the same cross-section, is achieved, for example, in a fiber bundle consisting of fibers according to the invention.

The invention also relates to the use of the regenerated cellulose fiber according to the invention and, respectively, of the fiber bundle according to the invention in absorbent products, sanitary products, in particular tampons, incontinence products, sanitary pads and panty liners, filling materials for blankets, cushions and sleeping bags, packings for foodstuff, in particular for meat products, papers, in particular filter papers, flock, clothing, in particular inlay fleece and clothing textiles for moisture management, mixed with other fibers or as a multi-layered structure, and wound dressings.

EXAMPLES

Y-Fibers for the production of absorbent bodies having a high absorption capacity are known from the prior art. By the wings existing in this case, the fiber centers are kept at a large distance from each other so that structures with a large liquid storage capacity emerge. However, the capillarity is limited due to the size of the pores that are formed. FIG. 1 shows the attachment of two conventional Y-fibers 1, 2 and the pore structure produced in this way.

The production of fibers having a flat cross-section is also known from the prior art. The sole use of flat fibers for absorbent bodies is not preferred since, due to their structure, they may be located very closely next to each other and the structures thus produced have only a minor absorption capacity, see FIG. 2, in which flat fibers 1′, 2′ (etc.) lying next to each other are depicted.

A further problem of flat fibers is that they can be bent about their thinner axis with relative ease. Therefore, hollow spaces in liquid-charged absorbent bodies collapse easily.

In the fiber according to the invention, a smaller pore size can now be achieved by appropriately arranging and dimensioning at least one, preferably several limbs diverging from the oblong section.

FIG. 3 shows a preferred embodiment of a fiber 1″ according to the invention comprising an oblong section 3 and several limbs 4, 5, 6, 7 diverging from the oblong section 3 essentially at a right angle, as is the case in FIG. 3. Said fiber can be produced by spinning a viscose spinning mass through a spinning opening having an appropriate configuration (i.e., a slot-shaped section and limb-shaped sections branching off from said section).

As shown in FIG. 3, the length of the limbs 4, 5, 6, 7 is in each case less than 40% of the length of the oblong section. The width of the limbs is in each case smaller than the width of the oblong section.

During the fiber processing according to the prior art, the fibers are parallelized at a certain rate. Therefore, the following consideration initially takes parallelized fibers as a basis.

The limbs of the structure produced from fibers according to the invention act as distance pieces which cause the formation of a large number of very fine capillaries when several such fibers are attached to each other (see FIG. 4).

Simultaneously, the limbs also act as a reinforcement and as distance pieces, which prevents a bending of the fiber across the thinner axis of the flat fiber portion. In this manner, a high absorption capacity is ensured.

A further advantage of the fiber according to the invention is that water is stored particularly advantageously by adhesion forces in the large number of clearances between the limbs of a fiber, which is illustrated in FIG. 5. Thus, structures made of the fibers according to the invention exhibit a particularly high water retention capacity against pressure. 

1. A regenerated cellulose fiber having a cross-section which comprises an oblong, essentially flat section having a length, wherein at least one limb branches off from the oblong section, and wherein said limb has a length that is at most 40% of the length of the oblong section.
 2. The cellulose fiber according to claim 1, wherein the at least one limb is arranged essentially at a right angle with respect to the oblong section.
 3. The cellulose fiber according to claim 1, comprising more than one branch-off limbs.
 4. The cellulose fiber according to claim 3, wherein the limbs branch off from the oblong section in more than one direction.
 5. The cellulose fiber according to claim 3, wherein the total length of the branch-off limbs does not exceed the length of the oblong section.
 6. The cellulose fiber according to claim 1 or 3, wherein at least one of the limbs has a ratio of length to width of from 2:1 to 10:1.
 7. The cellulose fiber according to claim 1 or 3, wherein at least one of the limbs has a width which is smaller than the width of the flat section.
 8. The cellulose fiber according to claim 1, wherein the entire curvature of the flat section has at most 120°.
 9. The cellulose fiber according to claim 1, wherein the fiber has a titer that ranges from 1.3 dtex to 10 dtex.
 10. The cellulose fiber according to claim 1, wherein the cellulose fiber is in the form of a fiber selected from the group consisting of a staple fiber, a short-cut fiber or a filament tow.
 11. A fiber bundle containing a plurality of regenerated multi-limbed cellulose fibers, wherein at least 10% of the multi-limbed cellulose fibers comprise a cellulose fiber according to claim
 1. 12. The fiber bundle according to claim 11, wherein the multi-limbed cellulose fibers have cross-sections that are essentially equal.
 13. A process for the production of a regenerated cellulose fiber according to claim 1, comprising the steps of providing a viscose spinning mass spinning the viscose spinning mass through at least one opening of a spinneret into a spinning bath, whereby filaments are formed, wherein the opening of the spinneret comprises a slot-shaped section from which the at least one limb branches, wherein the slot-shaped section has a length, and wherein the length of the at least one limb is at most 40% of the length of the slot-shaped section.
 14. The process according to claim 13 or 20, wherein the spinneret comprises several openings, with all the openings having essentially the same shape.
 15. A product comprising the regenerated cellulose fiber according to claim 1, wherein the product is selected from the group consisting of absorbent products, sanitary products, filling materials, packings for foodstuff, flock, clothing and wound dressings.
 16. The cellulose fiber according to claim or 6, wherein all of the limbs have a ratio of length to width of from 2:1 to 10:1.
 17. The cellulose fiber according to claim 7, wherein all the limbs have a width which is smaller than the width of the flat section.
 18. The fiber bundle according to claim 11, wherein at least 20% of the multi-limbed cellulose fibers comprise a cellulose fiber according to claim
 1. 19. The fiber bundle according to claim 18, wherein at least 50% of the multi-limbed cellulose fibers comprise a cellulose fiber according to claim
 1. 20. A process for the production of a fiber bundle according to claim 11, comprising the steps of providing a viscose spinning mass spinning the viscose spinning mass through at least one opening of a spinneret into a spinning bath, whereby filaments are formed, wherein the opening of the spinneret comprises a slot-shaped section from which the at least one limb branches, wherein the slot-shaped section has a length and wherein the length of the at least one limb is at most 40% of the length of the slot-shaped section.
 21. A product comprising the fiber bundle according to claim 11, wherein the product is selected from the group consisting of absorbent products, sanitary products, filling materials, packings for foodstuff, papers, flock, clothing, and wound dressings.
 22. The product according to claims 15 and 21, wherein the sanitary products is selected from the group consisting of tampons, incontinence products, sanitary pads and sanitary liners.
 23. The product according to claims 15 and 21, wherein the filling materials are filling materials for blankets, cushions and sleeping bags.
 24. The product according to claims 15 and 21, wherein the packings are meat packings.
 25. The product according to claims 15 and 21, wherein the papers are filter papers.
 26. The product according to claims 15 and 21, wherein the clothing is inlay fleece. 